Optimization of the cultural medium and conditions for production of antifungal substances by Streptomyces platensis 3-10 and evaluation of its efficacy in suppression of clubroot disease (Plasmodiophora brassicae) of oilseed rape

• Streptomyces platensis 3-10 was optimized for production of antifungal substances.
• Optimized medium: starch 3% peptone 0.75% yeast extract 0.025% soybean meal 1%.
• Minor and trace elements: K2HPO4·3H2O, KH2PO4, MgSO4·7H2O MnSO4·H2O and ZnSO4·7H2O.
• Optimized cultural conditions: 28 °C, pH 6.5, 150 rpm for 72 h.
• Isolate 3-10 was found to be an effective BCA against clubroot of oilseed rape.

This study was conducted to optimize the cultural medium and conditions for production of antifungal substances by Streptomyces platensis 3-10 and to evaluate its efficacy in suppressing Plasmodiophora brassicae (PB), the causal agent for clubroot of oilseed rape. The optimization was done using the one-factor-at-a-time (OFAT) method, followed by orthogonal designing. The optimized medium contained starch at 3% (w/v), peptone at 0.75%, yeast extract at 0.025%, soybean meal at 1% (w/v) and minor/trace elements (K+, Mg2+, Mn2+, Zn2+), initial pH 6.5. After incubation in this medium at 28 °C/150 rpm for 72 h, isolate 3-10 showed high antifungal activity. The cultural filtrates (CF3-10) produced an average inhibition-zone diameter of 50 mm against Aspergillus niger. The live spores and metabolites of 3-10 in CF3-10 or its crude extracts (CE3-10) suppressed PB infection of oilseed rape roots by 3–83%, compared to the treatment with PB alone. The efficacy was positively correlated (correlation co-efficiency: 0.9526–0.9873, P < 0.05) to the applied dose of each active component. Germination of PB resting spores was inhibited by 75% and 80% by CE3-10 (1000 μg/mL, w/v) and CF3-10 (5%, v/v), respectively. These findings suggest that S. platensis 3-10 is a promising biocontrol agent against PB.

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